1. Field of the Invention
The present invention relates to a magnetic sensing element, the electric resistance of which changes according to the relationship between the magnetization direction of a pinned magnetic layer and the magnetization direction of a free magnetic layer having a magnetization direction rotatable in response to an external field. In particular, the present invention relates to a magnetic sensing element that maintains a stable magnetization state exhibiting improved read characteristics such as prevention of side reading and the like.
2. Description of the Related Art
FIG. 36 is a partial cross-sectional view of a conventional magnetic element, such as a spin valve film, viewed from the face that opposes a recording medium. Hereinafter, this face is referred to as the “opposing face”. As shown in FIG. 36, the magnetic sensing element is constituted from a composite film 5 comprising an antiferromagnetic layer 1 composed of a PtMn alloy, a pinned magnetic layer 2 composed of a NiFe alloy, a nonmagnetic material layer 3 composed of Cu or the like, and a free magnetic layer 4 composed of a NiFe alloy; two hard bias layers 6 respectively disposed at the two sides of the composite film 5; and electrode layers 7. The magnetic sensing element is of a hard bias type.
According to the conventional structure shown in FIG. 36, the electrode layers 7 extend over part of the upper face of the composite film 5. A large longitudinal biasing magnetic field is supplied from the bias layers 6 so that a sensing current from the electrode layers 7 can be supplied to the sensitive region and not to a dead region that makes substantially no contribution to the magnetoresistive effect. The sensitive region and the dead region will be described later with reference to FIG. 10.
The element size, i.e., the size of the composite film 5, must be reduced in order to meet the trends toward narrower track width. However, photolithographic technology has reached its limit and it is now difficult to further reduce the size of the composite film. Moreover, as the element becomes smaller, the percentage occupied by the dead region in the element becomes higher, resulting in degraded sensitivity. Furthermore, the dead region is not completely insensitive. In particular, the magnetization of the dead region slightly rotates in response to an external field near the border between the dead region and the sensitive region. Such a change in magnetization in the dead region affects the magnetization of the sensitive region and causes side reading.
FIG. 37 is a partial cross-sectional view of another example of a conventional magnetic sensing element viewed from the opposing face. The magnetic sensing element is constituted from the antiferromagnetic layer 1, the pinned magnetic layer 2, the nonmagnetic material layer 3, the free magnetic layer 4, and two second antiferromagnetic layers 8.
The second antiferromagnetic layers 8 are disposed on the free magnetic layer 4. The second antiferromagnetic layers 8 are separated from each other in the track width direction (the X direction) by a predetermined gap therebetween. The magnetic sensing element shown in FIG. 37 is of an exchange bias type. As shown in FIG. 37, the gap between the second antiferromagnetic layers 8 is defined as the track width Tw.
According to this conventional structure, the length of the free magnetic layer 4 in the track width direction (X direction) is sufficiently longer than the track width Tw. When compared to that of a hard bias type described above, this structure has been expected to easily achieve better control of the magnetization direction of the free magnetic layer 4, which is adaptable to narrower track widths.
Note that the magnetization directions in side regions 4a of the free magnetic layer 4 are pinned in the X direction in the drawing by exchange anisotropic magnetic fields generated by the second antiferromagnetic layers 8. A center portion 4b of the free magnetic layer 4 is moderately magnetized so as to be rotatable in response to an external magnetic field.
However, the magnetic sensing element of an exchange bias type shown in FIG. 37 has the following problems. Since the magnetic sensing element utilizes the exchange coupling magnetic fields with the second antiferromagnetic layers 8 and the thickness of the free magnetic layer 4 is uniform, the center portion of the free magnetic layer 4 is magnetized only by exchange interactions occurring within the free magnetic layer 4 in order to achieve a single-magnetic-domain state. Thus, the thickness and the composition of the second antiferromagnetic layers 8 and the free magnetic layer 4 or the state of the interface between the free magnetic layer 4 and the second antiferromagnetic layers 8 must be optimized in order to generate an exchange coupling magnetic field of the proper magnitude. Moreover, when the thickness of tips 8a of the second antiferromagnetic layers 8 is small, as shown in FIG. 37, the exchange coupling magnetic fields generated between the free magnetic layer 4 and the second antiferromagnetic layers 8 become excessively small. This attenuates the magnetic pinning in the side regions 4a of the free magnetic layer 4. In particular, the magnetic pinning at the borders with the center portion 4b becomes significantly weak. As a result, read characteristics are degraded, i.e., the off-track characteristics are degraded and linearity can be no longer maintained.
It has been the general understanding that neither a magnetic sensing element of a hard bias type nor a magnetic sensing element of an exchange bias type can achieve proper control of the magnetization of the free magnetic layer 4 compatible with narrower tracks.